ITS: Fix GPU deterministic mode + refactoring

[f3sch]

Fixes two things for ITS GPU to be deterministic again.

AliceO2/Detectors/ITSMFT/ITS/tracking/GPU/cuda/TrackingKernels.cu

Line 87 in 8c94458

o2::gpu::CAMath::Min(ZBins - 1, utils.getZBinIndex(layerIndex + 1, zRangeMax)),

Takes ZBin which is constexpr 256 but should be taken from params which set it to 64.

AliceO2/Detectors/ITSMFT/ITS/tracking/GPU/cuda/TrackingKernels.cu

Line 1285 in 8c94458

nCells[iLayer] + 1, // num_items

Should be foundSeedsTable.size(), since we can find more seeds than nCells.
with this I get (although there still are some bins with ~0.01% difference in 10 pp TFs. Any idea why?

The rest is mostly a refactoring which mostly happened on-the-fly especially the clusterToTracksImpl since I wanted to be sure that both algorithms do not diverge at any point.

[github-actions]

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[alibuild]

Error while checking build/O2/fullCI_slc9 for 8be3ee5 at 2025-04-17 22:43:

## sw/BUILD/o2checkcode-latest/log
--
========== List of errors found ==========
++ GRERR=0
++ grep -v clang-diagnostic-error error-log.txt
++ grep ' error:'
/sw/BUILD/11921aa24f97e95c080dfce14a35f98fd40639b9/O2/Detectors/ITSMFT/ITS/tracking/GPU/hip/TrackingKernels.hip:802:85: error: use nullptr [modernize-use-nullptr]
/sw/BUILD/11921aa24f97e95c080dfce14a35f98fd40639b9/O2/Detectors/ITSMFT/ITS/tracking/GPU/hip/TrackingKernels.hip:815:90: error: use nullptr [modernize-use-nullptr]
/sw/BUILD/11921aa24f97e95c080dfce14a35f98fd40639b9/O2/Detectors/ITSMFT/ITS/tracking/GPU/hip/TrackingKernels.hip:821:85: error: use nullptr [modernize-use-nullptr]
/sw/BUILD/11921aa24f97e95c080dfce14a35f98fd40639b9/O2/Detectors/ITSMFT/ITS/tracking/GPU/hip/TrackingKernels.hip:834:90: error: use nullptr [modernize-use-nullptr]
/sw/BUILD/11921aa24f97e95c080dfce14a35f98fd40639b9/O2/Detectors/ITSMFT/ITS/tracking/GPU/hip/TrackingKernels.hip:898:84: error: use nullptr [modernize-use-nullptr]
++ [[ 0 == 0 ]]
++ exit 1
--

Full log here.

[alibuild]

Error while checking build/O2/fullCI_slc9 for 55f819d at 2025-04-18 12:04:

## sw/BUILD/o2checkcode-latest/log
--
========== List of errors found ==========
++ GRERR=0
++ grep -v clang-diagnostic-error error-log.txt
++ grep ' error:'
/sw/BUILD/11921aa24f97e95c080dfce14a35f98fd40639b9/O2/Detectors/ITSMFT/ITS/tracking/GPU/hip/TrackingKernels.hip:802:85: error: use nullptr [modernize-use-nullptr]
/sw/BUILD/11921aa24f97e95c080dfce14a35f98fd40639b9/O2/Detectors/ITSMFT/ITS/tracking/GPU/hip/TrackingKernels.hip:815:90: error: use nullptr [modernize-use-nullptr]
/sw/BUILD/11921aa24f97e95c080dfce14a35f98fd40639b9/O2/Detectors/ITSMFT/ITS/tracking/GPU/hip/TrackingKernels.hip:821:85: error: use nullptr [modernize-use-nullptr]
/sw/BUILD/11921aa24f97e95c080dfce14a35f98fd40639b9/O2/Detectors/ITSMFT/ITS/tracking/GPU/hip/TrackingKernels.hip:834:90: error: use nullptr [modernize-use-nullptr]
/sw/BUILD/11921aa24f97e95c080dfce14a35f98fd40639b9/O2/Detectors/ITSMFT/ITS/tracking/GPU/hip/TrackingKernels.hip:898:84: error: use nullptr [modernize-use-nullptr]
++ [[ 0 == 0 ]]
++ exit 1
--

Full log here.

[mconcas]

Hi, thanks for looking into this. As per usual it would be better to separate code refactoring from small fixes. Can you split it in two?

[f3sch]

Sure, now first commit is the actual fix, second the refactoring work done in GPU kernel code, the third is the refactoring of the hybrid/cpu call chain.

[f3sch]

Now it is up to the precision of TH1F identical :)
20 TFs in both of high IR pp.